Disable "descending" parameter for documents filter.

Because we won't be able to support it with all_docs replacement.

Change-Id: Ia8d956ef3a5993fa6ecf5808f7ac9848f480b769
Reviewed-on: http://review.couchbase.org/34662
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>